The objective of this research is to further explore the importance of two proteins which we have recently purified from sea urchin actin gels. We seek to understand the biochemistry of these proteins and want to know, at the cellular level, where they are located and what functions they serve in cell motility. The specific objectives of the proposal are: a. To extend our biochemical studies on the association of actin with these two key proteins which are required for actin fibril formation and actin gelation in eggs. b. To localize these two actin crosslinking proteins, using indirect immunofluorescence techniques, in sea urchin eggs, muscle and coelomocytes and to look for changes in their distribution after fertilization and during cell division. c. To isolate and purify the regulatory proteins which make actin gelation sensitive to low concentrations of calcium ions. This will be done using a newly developed fluorescent actin assay method. d. To extend our studies on the effects of purified rabbit muscle proteins on actin gelation in order to further define the actin binding sites for these crosslinking proteins. e. To look for similar actin associated proteins in other invertebrate and vertebrate cells.